Emanuel "Manny" Shinwell became a national hero for the Scottish left when he helped lead the workers' revolt of 1919 – which only ended when Winston Churchill ordered British tanks into Glasgow's George Square.
However, historian Jacqueline Jenkinson in a new book has unearthed evidence she says shows that Shinwell encouraged mobs to attack black sailors.
Jenkinson, in Black 1919, also reveals that Shinwell's radical seamen's union, the BSU, banned black members, many of whom had fought for Britain in the recently ended Great War.
She said: "There has been a reluctance to accept that many of the Red Clydesiders promoted actions that were discriminatory and unfair to the black sailors."
Jenkinson's claims sparked a furious response from surviving relatives. His nephew, Sir Adrian Shinwell, a prominent lawyer and former chief executive of the Conservative Party in Scotland, said: "I find this utterly bizarre."
Shinwell went on to become a minister in Clement Attlee's government of 1945 and 1951 and a member of the House of Lords.